The invention relates to a multistage compressor, and more particularly to a refrigeration system for use in such multistage compressor.
Compressors, particularly rotary compressors, have been used in different fields of engineering, especially in air conditioners and refrigeration systems. These compressors mostly use chlorides containing refrigerants such as R-22 (hereinafter referred to as Freon gas).
However, Freon gas is known to destroy the earth""s ozone layer and its use is now legally regulated. Hence, extensive researches have been made for an alternative refrigerant that poses no such problem. In this regard, carbon dioxide is anticipated to be a good candidate.
A type of rotary compressor is known, which utilizes carbon dioxide as a refrigerant (carbon dioxide will be hereinafter simply referred to as refrigerant unless it needs to be distinguished from other refrigerants) in a multistage compressor incorporating multiple compression elements.
Such multistage compressor comprises multiple compression elements for sucking, compressing, and discharging the refrigerant; a drive element for driving these compression elements, and a housing for accommodating the compression elements and the driving element.
Each of the multiple compression elements includes a roller which is fitted on an eccentric cam formed integral with a rotary shaft of the driving element and rolls on the inner wall of a cylinder. The space between the roller and the cylinder is divided into a suction chamber and a compression chamber by a vane that abuts on the roller. The multiple compression elements are adapted to sequentially perform suction, compression, and discharge of the refrigerant in multiple stages.
The driving element comprises an electric motor for rotating the shaft of the compression elements. These elements are all housed in a closed container.
However, in such a conventional multistage compressor as mentioned above, the atmosphere surrounding the driving elements does not flow, so that heat generated by the driving element stays inside the closed container, thereby raising the temperature of the driving element, which in turn hinders necessary compression of the refrigerant. This is a serious problem for apparatuses that utilize such compressor.
In other words, heat generated by the driving element must be radiated to the surroundings through the closed container, but it has become increasingly difficult to install a heat removing fan for removing heat from the compressor in a space around the compressor in order to meet a recent commercial request for an ever compact compressor.
Therefore, it has been an important matter in the design of a compressor to implement a mean for effectively radiating the heat generated by the driving element out of the closed container, hopefully without affecting the environment. A satisfactory solution, however, has not been found.
In order to overcome prior art problem as mentioned above, the invention provides a multistage compressor capable of efficiently suppressing heating of the driving element.
In accordance with one aspect of the invention, there is provided a multistage compressor having more than one compression elements for compressing a refrigerant, and a driving element for driving said compression elements, said driving element and said compressing elements accommodated in an enclosed container, said multistage compressor characterized in that the refrigerant is adapted to cool the driving element after the refrigerant is discharged from one of the compression elements and before it returns to the compression element in the next stage.
Thus, with such a simple arrangement of the compressor, the temperature rise of the driving element is efficiently suppressed.
Specifically, in one embodiment, a multistage compressor of the invention includes a closed container, a driving element in the form of an electric motor securely fixed in the upper section of the closed container; a two-stage compression element, provided in the lower section of the container, consisting of a first stage compression element and a second stage compression element which are driven by respective eccentric cams mounted on the shaft of the motor, characterized in that
a connection tube is connected to the upper section of the closed container which extends outwardly therefrom and returns to the inlet of the second stage compression element through the lower section of the container;
the refrigerant taken in the first stage compression element is compressed to an intermediate pressure (said refrigerant referred to as intermediate pressure gas) and discharged therefrom into the inner space of the closed container to cool the driving element;
the intermediate pressure gas is returned to the second stage compression element through the connection tube; and
the intermediate pressure gas is further compressed to a high pressure and discharged therefrom by a second stage discharge tube.
Instead of directly discharging the intermediate pressure gas from the first stage compression element into the inner space of the closed container, the gas may be alternatively discharged into the lower section of the closed container through a first stage connection tube which is connected to the outlet of the first stage compression element and extends once out of the container and returns to the lower section of the container.
Further, an additional refrigeration unit may be provided at an intermediate point of the first stage connection tube, or of the second stage connection tube, to enhance heat radiation from the refrigerant, which helps increase the amount of the gas sucked into the second stage compression element, thereby improving the compression efficiency.